The invention relates to a zener diode having a semiconductor body with a surface zone doped with more than 10.sup.18 atoms/cc in which at least two regions are provided through diffusion with substantially the same concentration of doping atoms, which regions adjoin a surface of the surface zone and form p-n junctions with the surface zone, a first region having a smaller lateral cross-section and a smaller depth than a second region and both regions being connected to a first connection electrode provided on the surface, while a second connection electrode, which is spaced apart from regions, is provided on the semiconductor body.
A zener diode as described above has a comparatively low zener voltage of below approximately 10 V because of the comparatively high concentration of doping atoms of the surface zone. The smaller diode formed by the first region, which is also called the reference diode, has a lower zener voltage than the larger diode formed by the second region and called the protective diode. In a practical embodiment, the first region has a cross-section of, for example, 1000 .mu.m.sup.2 and a depth of 1 .mu.m, whereas the second region has a cross-section of 10000 .mu.m.sup.2 and a depth of 1.5 .mu.m. At a comparatively small current of, for example, 250 .mu.A through the zener diode, the reference diode alone will conduct. At higher currents of, for example, 100 mA the current flows substantially entirely through the protective diode. Since the reference diode has a comparatively small cross-section, the current density through this diode is comparatively great at a current of 250 .mu.A. As a result, the zener diode has a comparatively steep current-voltage characteristic at this low current of 250 .mu.A.
French Patent Application no. 81 05 132 discloses a zener diode of the kind mentioned in the opening paragraph in which an annular second region surrounds a disc-shaped first region, while the regions overlap partly. The second region is formed from a highly doped polycrystalline silicon layer in the shape of a ring by means of a comparatively deep diffusion. The first region is formed in that a second highly doped epitaxial silicon layer is provided, overlapping the polycrystalline layer, upon which the first region is formed through shallow diffusion.
Although the known zener diode described has a current-voltage characteristic which is much steeper than that of a standard zener diode, the steepness of the current-voltage characteristic is not sufficient for some applications.